Thomasaria ventosa, Baliński, 2006

Baliński, Andrzej, 2006, Brachiopods and their response to the Early-Middle Frasnian biogeochemical perturbations on the South Polish carbonate shelf, Acta Palaeontologica Polonica 51 (4), pp. 647-678 : 672-674

publication ID	https://doi.org/ 10.5281/zenodo.13748597
persistent identifier	https://treatment.plazi.org/id/03BE87A9-FFD9-FF80-A564-F98FE0707AA5
treatment provided by	Felipe
scientific name	Thomasaria ventosa
status	sp. nov.

Treatment

Thomasaria ventosa sp. nov.

Fig. 19A, B View Fig .

Holotype: Complete shell ZPAL Bp 60/10 ( Fig. 19A View Fig ).

Type horizon: Complex C, layer 60, Palmatolepis transitans conodont

Zone. Type locality: Wietrznia Ie quarry, SE part of city of Kielce; N 50°

51’21.0’’, E 20°38’30.6’’.

Derivation of the name: From Latin ventosus —windy, to indicate that the material was collected at Wietrznia hill, which name suggests prevailing windy weather condition.

Diagnosis.—About medium−sized for the genus, wider than long, with rounded cardinal extremities; strongly semipyramidal ventral valve, slightly concave to slightly arched in lateral profile; very high, usually flat procline ventral interarea; without fold and radial ribs, wide sulcus with median furrow. From Thomasaria warreni Cooper and Dutro, 1982 differs by having much higher and mostly flat ventral interarea. From T. demissa Cooper and Dutro, 1982 it is much wider. T. rockymontana ( Warren, 1928) and T. altumbona Stainbrook, 1945 have stronger dorsal fold and radial ribs.

Material.—Wietrznia Id−W: one complete shell and two fragments from bed 4a, two incomplete ventral valves from bed 4g. Wietrznia Ie: three ventral valves embedded in rock from beds 29–30, one complete shell from bed 60, one ventral valve from bed 66, and one incomplete ventral valve from bed 90.

Description.—Shell medium sized for the genus, wider than long, transversely elliptical, strongly ventribiconvex; anterior commissure uniplicate, anterior margin slightly emarginate, both valves smooth without perceptible ribs; hinge margin straight and wide, slightly narrower than maximum shell width, lateral margins rounded, cardinal extremities rounded to angular.

Ventral valve semipyramidal, usually straight to concave, rarely very slightly convex in lateral profile, with convex flanks transversally but straight to slightly concave longitudinally; interarea very long, procline, flat to rarely slightly concave, may be convex in its apical part, its lateral borders form an angle 40–85°; delthyrium narrow, attaining 13–20°; sulcus arises on the umbo, rather shallow but deepened medially with a furrow, wide, occupying 58–62% of the shell width, poorly bounded laterally except at the anterior margin where slightly angular sulcus borders are marked; beak sharply pointed, slightly asymmetrical apically, frequently slightly deflected anteriorly.

Dorsal valve shallow and gently convex; fold imperceptible but the median sector of the valve somewhat deflected close to the margin, suggesting inception of the fold.

Interior of the ventral valve with strong highly divergent dental palates. Apical part of the delthyrium covered by a pair of apical plates. Deltidial plates may also be developed in anterior half of the delthyrium. Shell substance impunctate.

Pustulose microornamentation preserved on one specimen only.

Intraspecific variability.—The specimens here studied display great variability in general shape of the shell as well as in development of the ventral interarea. This condition seems to be characteristic for species of the genus ( Davidson 1864 –1865; Crickmay 1967; Baliński 1979; Cooper and Dutro 1982). Some of the specimens from beds 29–30 of Wietrznia Ie section have strongly flattened, triangular flanks and median sector of the ventral valve which in combination with high, flat interarea give the valve almost regular shape of a prism with rectangular base. Highly variable is also shape of the ventral interarea expressed in an angle formed by its lateral borders. Among three ventral valves from the beds 29–30 the angle varies from 40 to 78°. The highest measured value of the angle is 85° attained by the specimen from bed 4 of Wietrznia Id−W section.

Remarks.—This species differs externally from Spirifera simplex Phillips, 1841 from the British Devonian by shell dimensions mainly attaining one third of the shell width of the latter. The Polish specimens also possess wider ventral sulcus deepened medially with longitudinal furrow. Nalivkin (1947) erected genus Pyramidalia with S. simplex as a type species. The genus was put in synonymy with Squamulariina Frederiks, 1916 by Carter et al. (1994) implying possession of spondylium and punctate shell in Phillips’ (1841) species. This, however, seems doubtful as Nalivkin (1947: 124) mentioned the presence of dental plates in Pyramidalia simplex . Thus, if the presence of dental plates and impunctate shell in type specimens of Spirifera simplex will be acknowledged, then the species may belong more probably to Thomasaria instead ( Baliński 1979).

The most similar species to the new one here described are: Thomasaria rockymontana ( Warren, 1928) , T. altumona Stainbrook, 1945 , T. demissa Cooper and Dutro, 1982 , and T. warreni Cooper and Dutro, 1982 , all from the Frasnian of North America. The new species differs from T. warreni by having much higher and most often flat, not concave ventral interarea and flat ventral valve in lateral view which in the latter is quite strongly arched. T. demissa is much wider than T. ventosa sp. nov. and has generally pointed cardinal extremities. T. rockymontana and T. altumbona possess better expressed dorsal fold and radial ribs as well as arched ventral valve in lateral profile. The specimens from the Frasnian of the Dębnik anticline (southern Poland) described as T. simplex by Baliński (1979) are quite similar to the new species but differ by having better marked radial ribs and usually slightly concave ventral interarea ( Fig. 19C View Fig ).

Occurrence.—This is uncommon species in the Frasnian brachiopod fauna from Wietrznia quarry; it was recovered in Id−W and Ie sections (Figs. 2, 3). One incomplete shell recently recovered from the top−most layers of the northern quarry at Dębnik (southern Poland) is illustrated here as Thomasaria sp. for comparison ( Fig. 19C View Fig ).